forces in bolts connecting sister members

[smulmi]

Hi all,

I am designing a repair of a wooden beam by sistering it with steel channels on its side. The channels are to be connected to the wood member by through bolts. What are the forces that I need to consider while designing the through bolts for composite action of wood and steel channels like vertical shear, shear flow etc?

Thanks in advance,

Sarju

 

[JAE]

If the two channels can take all the load, then I wouldn't worry about composite action. Just have bolts enough to transfer the load per foot into the channels.
If the channels are also directly underneath decking or joists that transfer load into the original beam, then you probably don't need bolts at all other than to stabilize or brace the channels.

 

[smulmi]

Thanks JAE,

The channels do not run the full length of the beam and are only to be provided partially at the mid span. Also the ceiling is hung from the bottom of the beam and the wood beam is deeper than the channels with the top of both members being almost flush.

Sarju

 

[PUEngineer]

This sounds a little funky to me, but I don't do much with timber framing, let alone repair of timber framing. Can you explain why the repair is needed? Is there loading on the damaged beam now?

 

[woodman88]

One problem is the wood beam to composite beam transfer of forces. I would not do a wood/steel composite beam. Rather I would design the steel beam for the full load. If you can not extend the steel to the bearing. I would design a connection to transfer the load from the steel beam to the wood beam. In any case the required connection at the ends of the steel channels to the wood member is a moment connection. I am always conservative with moment connects in wood.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[IsaacStructural]

I'm really curious how this system works. To get the steel and wood to act compositely you'll need to ensure stiffness compatibility as well as load transfer.

Look for a flitch beam design example, should give you an idea of the appropriate calculations and checks you need to do.

For this sort of thing, I'd probably look to add a new topping wood member and through bolt it to existing, again considering shear flow to get the new deeper member to act compositely.

M.S. Structural Engineering
Licensed Structural Engineer and Licensed Professional Engineer (Illinois)